Tilting platform checkweighing device

ABSTRACT

A checkweighing station includes a weigh platform mounted on a load cell which in turn is mounted on a rotatable shaft so that the entire assembly can be rotated to tilt the platform in one direction for an acceptable weight of a weighed item and in another direction for a rejected weight or weight of a different catgegory. A memory device can determine a trend and make adjustments in a production process.

RELATED APPLICATION

This application claims the full benefit of Provisional ApplicationSerial No. 60/197,465 filed Apr. 17, 2000 having the same title.

BACKGROUND OF THE INVENTION

There is a need for an efficient device for accepting or rejecting, byweight, similar articles that are delivered to a weighing device. Inparticular, there is a need for a system for checkweighing similararticles and containers which are to meet specified weight criteria, andseparating, at the point of weighing, those that meet the criteria fromthose which do not.

A 1914 patent to Sloan and Barnes, U.S. Pat. No. 1,089,680, describes aweighing system for quality control of cigarettes based on weight,wherein the rate of manufacture is regulated according to whether thecigarettes are within specification. Drums are rotated for filling anddischarge according to the weight of their contents, inVogel-Jorgensen's U.S. Pat. No. 2,055,131.

A simple platform on a load cell is proposed by Lumby et al for weighingfowl, in U.S. Pat, No. 3,780,818. Mims, in U.S. Pat. No. 4,155,549,sorts heavier and lighter balls by combining a diverting plate with apivotable weighing plate. A hopper is actuated by Okada for releasingobjects heavier than a preset value, in U.S. Pat. No. 5,611,437. And,Shaanan et al, in U.S. Pat, No. 5,708,236, describe a cantilever beamfor transmitting force, i.e. weight, to a strain gauge.

It is not uncommon to employ a weigh station in a production conveyingline for determining whether the produced items are too heavy or toolight, wherein the system automatically diverts an out-of-specificationitem from the conveying line at a point downstream from the weighstation. The actual weighing can take place as the item is moving or ina static condition, but in either case the diversion or separationtypically is conducted at a point further removed from the weighstation. See, for example, Kvisgaard et al U.S. Pat, No. 5,998,740,Tokutu U.S. Pat, No. 5,383,561, Beauchemin et al U.S. Pat, No.5,006,225, Rice et al U.S. Pat, No. 3,139,184, and Altenpohl et al U.S.Pat. No. 3,596,749.

I am not aware, however, of a system of the type described below,wherein an object is weighed on a weigh platform which itself is tiltedimmediately to divert the object when it is too heavy or too light.

SUMMARY OF THE INVENTION

My invention is useful in production lines, particularly those having aconveying system and wherein weight specifications are important. It isa checkweighing system wherein a newly produced or other item is placed,as by a robot arm, on a weigh platform, the item is weighed, and, if itis outside a desired weight range, the platform is tilted to cause theitem to slide or fall into a bin or onto a diverting conveyor. Myinvention is quite versatile, in that the weigh interval or time, thespeed of the tilt, and the degree of the tilt can be readily adjusted.My system will not only accept or reject the production items one at atime, but can discern trends and be used otherwise to adjust productionpractices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a more or less diagrammatic sectional view of my weighstation, showing the horizontal platform.

FIG. 2 is a view similar to that of FIG. 1, but with the platform tiltedto reject an item.

FIG. 3 shows a preferred construction of a platform, load cell beam, androtatable shaft to which the load cell beam is fixed.

FIG. 4 is a flow sheet or logic diagram showing the overall processfollowed by a preferred version of my invention.

FIG. 5 shows another preferred version of my invention using a differenttype of load cell.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a platform 1 is fastened by bolt 2 to load cell beam 3 whichcontains a load cell not seen. Framework 4 and housing 5 supportrotatable shaft 6, onto which the beam 3 is fixed.

FIG. 2 is a view similar to that of FIG. 1 except that the platform 1has been tilted by rotating shaft 6, which also tilts beam 3. Rotationof shaft 6 and tilting of platform 1 enables the mechanism to reject anitem on the platform 1. Rotation of shaft 6 and tilting of platform 1 isdepicted for rejection, but a similar rotation and shifting in the otherdirection is performed for acceptable items. The appropriate directionis determined by the controller 10, seen in FIG. 4. When the item hasbeen removed by gravity from the platform, the shaft is again rotated,in the opposite direction from that used for rejection or acceptance,and the platform is returned to the horizontal, ready to receive thenext item, which will be placed on it by an arm or other mechanism notshown. For proper operation of contemporary load cells and load cellbeams, the platform should be substantially horizontal, preferablywithin five arc minutes of horizontal. As indicated below, however, myinvention contemplates the use of any load cell beam or direct weight(vertical force) load cell or strain gauge capable of accuratelyweighing an item on platform 1 and generating a signal representative ofthe weight of the item within a desired tolerance.

FIG. 3 reveals the preferred assembly of FIGS. 1 and 2 in a differentsectional view. Here it is seen that platform 1 is fixed by bolts 2 toload cell beam 3 and load cell beam 3 is fixed to shaft 6. Shaft 6 mayrotate in a bearing or collar in housing wall 12. Load cell beam 3 isfixed to shaft 6 so that it will turn with shaft 6 when it is turned bya motor 14 outside of housing wall 12. Shaft 6 may also be supported byhousing wall 13, preferably in a bearing permitting easy rotation.Spring 15 helps to stabilize load cell beam 3. In this preferredconfiguration, the load cell beam 3 is a single point aluminum load cellmodel MT083286020 provided by Mettler-Toledo. The load cell or a similarconstruction may accommodate strain gauges of varying capacities, but inthis type of load cell, the strain gauges are placed within the loadcell beam 3 and calibrated so that variations in positioning of theitems on the platform will not significantly affect the weightdetermination.

The load cell beam is of a type readily available commercially. Thestrain gauges within the load cell are positioned and calibrated todetect stress in the beam caused by the leverage of the weight at theplatform and through the point of attachment to shaft 6. The load cellbeam 3 is capable of weighing an item on the platform 1 and generating asignal representing the weight of the item. My invention utilizes thissignal for comparison to a standard or set point to cause the platform 1to be tilted in a predetermined direction when the item exceeds apredetermined weight or is under a predetermined minimum weight. If theitem is within the acceptable limits the platform 1 is tilted in theother direction. When the platform 1 is tilted in either direction, theitem descends into a bin or onto a conveyor for further handling.

Probably the most common load cell beam 3 of the type described has acapacity from 10 grams to 4000 grams, although other ranges areavailable—for example having maximum capacity of 1000 g, 3000 g, and5000 g and being reliably accurate within varying tolerances such as0.05 g, 0.1 g, and 0.2 g. I do not intend to be limited to such rangesand accuracies, as the principle of my invention is clearly applicableto other ranges and accuracies.

FIG. 4 is a flow sheet showing the logic of the system, which may beaccomplished with various types of control systems known in the art. Inthe ideogrammatic flow sheet of FIG. 4, a production area 30 or othersource provides items to be checked for quality control. The items aremoved onto weigh station 31 by a mechanical arm (not shown) or othersuitable device, where they are weighed. Weigh station 31 is preferablydesigned as illustrated in FIGS. 1-3 or 5, and generates an electricalsignal as a function of the weight of the item. Comparison of the weightmay be performed in a simple comparator having a set point or may bedone in microprocessor 32. A control signal is generated by controller10 according to whether the weight is within an acceptable range,causing motor 33 to tilt the weigh platform 1 to the right or left,after which it is returned to horizontal. Microprocessor 32 will acceptoperator-controlled inputs for adjusting the tilt angle and the weighinginterval or duration (for example, the interval between tilting andreturning to horizontal), and preferably will accumulate data on theincidence of non-conforming items adequate to detect trends. Forexample, in a facility manufacturing items by compression powdermetallurgy, an incidence of two or three underweight items in fortymight trigger an automatic increase in pressure along with a slightpredetermined increase in the amount of powdered metal for each itemmade.

The load cell beam 3 (FIGS. 1, 2, and 3) is preferred because it iscommercially available and its specifications are readily used in mysystem. However, it is not necessary to use a beam; rather, the loadcell may be located directly under the platform and fixed to the shaftin vertical alignment so that the point of attachment to the shaft isdirectly under the center of the platform, as shown in FIG. 5. FIG. 5 isan alternative construction in which platform 1 is fixed to and locateddirectly above load cell 40, which in turn is fixed to shaft 6 invertical alignment to the center of platform 1. This requires the use ofa load cell which is sensitive to downward force (as differentiated fromtorque stress as detected by a beam-type load cell). It will be able tocompensate for placement of items to be weighed in locations not exactlyin the center of platform 1. Such a load cell will detect an off-centerplacement of a load and compensate for a possibly unsymmetricalcharacter of the downward force, generating an accurate weight signal inspite of placement of the item to be weighed in a location other thanthe center of the platform. Persons skilled in the art may considermultiple load cell or strain gauge constructions built to measuredownward or gravitational forces on a plurality of points of ahorizontal platform due to the non-central placement of items of theplatform. My invention contemplates the use of any such strain gauges orload cells, so long as they are able to generate a signal accuratelyrepresentative of the weight of the item placed on the platform.

It should be noted that the preferred constructions shown in FIGS. 1, 2,3, and 5 utilize a load cell located substantially in the center of theplatform 1 and that the shaft 6 passes substantially directly undercenter of platform 1 so that the axis of rotation of the assembly isunder the center of the platform 1.

My invention also contemplates adjustable tilting angles and adjustablespeed of tilting. These parameters may be preset in controller 10 orcontrolled more elaborately by microprocessor 32. Microprocessor 32 mayalso be programmed to detect trends in the production process such as,for example, an increase in the number of rejections over apredetermined period of time or a predetermined number of items weighed.As an example, the microprocessor or other memory device may beprogrammed to generate a warning signal or a control signal if more thantwo of the last previous 40 items were out of specification. Correctiveaction may then be taken manually or automatically.

Thus it is seen that my invention contemplates apparatus for acceptingor rejecting items by weight comprising a substantially horizontalplatform for holding items to be weighed, a beam supporting the platformat a first end, the beam including a single point load cell and beingmounted on a pivot at a second end, the load cell being capable ofgenerating a signal as a function of weight of an item on the platform,and means responsive to the signal for tilting the platform and the beamon the pivot when the item is outside of a desired weight range andreturning the platform to its original substantially horizontalorientation.

My invention also includes a method of controlling quality by weight ofsimilar items comprising placing an item in a substantially horizontalweigh area of a weigh station, weighing the item by a load cell in theweigh station and generating a signal representing the weight of theitem, comparing the signal representing the weight to at least onepredetermined standard therefor, generating a control signal ACCEPT orREJECT therefor, tilting the weigh area to permit gravity to remove theproduced item therefrom in one direction or another according to theACCEPT or REJECT signal, and returning the weigh area to a substantiallyhorizontal orientation. Persons skilled in the art will recognize thatthe labels ACCEPT and REJECT need not be taken literally—that is, theymay simply represent two different weight categories for sorting.

In addition, my invention includes apparatus for accepting or rejectingitems by weight comprising a weigh station including a platform havingan area for holding an item to be weighed, a load cell under theplatform, the load cell being capable of generating a signal as afunction of weight of an item on the platform, and a controllerresponsive to the signal for tilting the platform and the load cell whenthe item is outside of a desired weight range and returning the platformto its original orientation.

What is claimed is:
 1. Checkweighing apparatus for accepting orrejecting items by weight comprising a weigh station in a fixedstationary location including a platform at said fixed stationarylocation having an area for holding an item to be weighed, a load cellunder said platform, said load cell for generating a signal as afunction of weight of an item on said platform, and a controllerincluding a motor responsive to said signal for tilting said platformand said load cell to remove said item from said platform at said fixedstationary location when said item is outside of a desired weight rangeand returning said platform to its original position.
 2. Apparatus ofclaim 1 wherein said controller includes a rotatable shaft passingsubstantially directly under said area for holding an item.
 3. Apparatusof claim 1 wherein said controller includes a microprocesor including atrend detector for generating a signal as a function of a statisticaltrend of weights of successive items.
 4. Apparatus of claim 3 includingmeans responsive to said trend signal for adjusting a production step asa function thereof.
 5. Checkweighing apparatus for accepting orrejecting items by weight comprising a weigh station in a fixedstationary location including a platform at said fixed stationarylocation having an area for holding an item to be weighed, a load cellmounted on a beam under said platform, said load cell for generating asignal as a function of weight of an item on said platform, and acontroller responsive to said signal for tilting said platform and saidload cell to remove said item from said platform at said fixedstationary location when said item is outside of a desired weight rangeand returning said platform to its original position.
 6. Checkweighingapparatus for accepting or rejecting items by weight comprising a weighstation in a fixed stationary location including a platform at saidfixed stationary location having an area for holding an item to beweighted, a load cell under said platform, said load cell for generatinga signal as a function of weight of an item on said platform, said loadcell being mounted substantially directly under its point of attachmentto said platform, and a controller responsive to said signal for tiltingsaid platform and said load cell to remove said item from said platformat said fixed stationary location when said item is outside of a desiredweight range and returning said platform to its original position. 7.Weighstation apparatus for accepting or rejecting items by weightcomprising (a) a substantially horizontal platform for holding items tobe weighed (b) a beam supporting said platform at a first end thereofsaid beam including a single point load cell and being mounted on apivot at a second end, said load cell for generating a signal as afunction of weight of an item on said platform, and (c) means responsiveto said signal for tilting said platform and said beam on said pivotwhen said item is outside of a desired weight range and returning saidplatform to its original substantially horizontal orientation, saidplatform, said beam, and said means for tilting being fixed in astationary location.
 8. Apparatus of claim 1 wherein said substantiallyhorizontal platform comprises a substantially flat surface.
 9. Apparatusof claim 1 wherein said substantially horizontal platform comprises acontainer designed to hold an item in a substantially fixed locationwith respect to said load cell.
 10. Apparatus of claim 1 wherein saidmeans for tilting said platform is a stepper motor.
 11. Apparatus ofclaim 1 wherein said means for tilting said platform is a pneumaticcylinder.
 12. Apparatus of claim 1 wherein said original substantiallyhorizontal orientation is within 5 arc minutes of horizontal. 13.Apparatus of claim 1 having a capacity of 500 grams to 100 kilograms.14. Apparatus of claim 1 including means responsive to said signal fortilting said platform and said beam on said pivot when said item iswithin said desired weight range, in a direction other than that whensaid item is outside said desired weight range, and returning saidplatform to its original substantially horizontal orientation.